Aviation superfuel



Patented Sept. 17, 1946 AVIATION SUPERFUEL Robert F. Marschner, Homewood, Ill., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana No Drawing. Application July 1, 1942, Serial No. 449,319

(Cl. M -80) 1 Claim. 1

This invention relates to a new'and improved superfuel, particularly for aviation combat and pursuit purposes and for other purposes where high output per unit weight engines are required, for example tank engines. It pertains more particularly to aviation fuels having greatly desired characteristics including both a high supercharge octane number and a high rich mixture response.

In order for aviation fuels to be fit for modern aviation engines, they mus-t meet certain basic characteristics with regard to volatility, both initial and overall, and in addition it is highly desirable that the aviation fuel exhibit maximum antiknock values under all conditions of use.

Broadly I propose to attain these desirable characteristics by adding to an aviation fuel base stock such as commercial isooctane, a. substantial pro portion of a unique aviation fuel component broadly defined as an alkylcycloalkane having less than eight and more than four carbon atoms in the molecule and comprising alkylcyclopropanes and alkylcyclobutanes. More specifically I propose blends containing l,l,2--trimethylcyclopropane and a commercial. isooctane as an excellent aviation fuel, both as such and with the addition of a small amount of an antiknock agent such as tetraethyl lead. A

A primary object of my inventionis to provide an aviation fuel component. which shows both a high supercharge octane number and a high rich mixture response. Another object is to provide a fuel which will operate efficiently during cruising and perform satisfactorily under take-off and combat conditions. A further object of my invention is to provide a blended aviation fuel of .improved distribution of antiknock properties throughout the boiling range and balanced antiknock characteristics with respect to changes in fuel-air ratios.

My proposed aviation fuels admirably fulfill these and other objects in that they possess the volatility characteristics desired, both the initial and the overall volatility, and at the same time have substantially similar high antiknock characteristics throughout the boiling range of the fuel. Thus when operating conditions are encountered where incomplete vaporization of the fuel occurs, the portion vaporized will have antiknock characteristics suitable for operation of the engine. The proposed aviation fuel has both excellent lean or standard condition antiknock properties and rich condition antiknock properties.

Broadly my invention contemplates the alkylcycloalkanes having more than four and less than eight carbon atoms to the molecule and having the general formula RnX wherein R represents an alkyl group having less than five carbon atoms, n is a whole number less than five, and X represents a cycloalkane ring having three or four carbon atoms. Particularly useful alkylcycloalkanes are those wherein the alkyl substituent or substituents R in the above formula have the general formula wherein C represents a carbon atom and K. L, and M are selected from. the class consisting of hydrogen atoms and methyl groups, i. e. a substituent selected from the class consisting of methyl, ethyl, isopropyl and tertiary butyl groups. Also of particular value is a group of alkylcycloalkanes in which the number of carbon atoms in the ring does not exceed n by more than one, for example the dito tetramethylcyclopropanes and the trimethylcyelobutanes. The two valuable types make up alkylcycloalkanes in which the longest straight ,chain in both ring and alkyl group which can be written does not exceed 5 carbon atoms.

Examples of C5, C6 and C7 naphthenes having three and four carbon atoms in the ring include the following:v

Ethyl cyclopropane, 1,1 dimethyl cyclopropane, 1,2 dimethyl cyclopropane, propyl cyclopropane, isopropyl cyclopropane, l-methyLl-ethyl cyclopropane, 1-methyl-2-ethyl cyclopropane, 1,1,2- trimethyl cyclopropane, 1,2,3-trimethyl cyclopropane, n-butyl cyclopropane, isobutyl cyclopropane, secondary butyl cyclopropane, tertiary butyl cyclopropane, l-methyl-l-propyl cyclopropane, l-methyl f l-propyl cyclopropane, l-methyl 1-isopropyl cyclopropane, l-methyl-Z-isopropyl cyclopropane, 1,1-diethy1 cyclopropane, 1,2-diethyl cyclopropane, 1,1-dimethyl-2-ethyl cyclopropane, 1,2-dimethy1-1-ethyl cyclopropane, 1,2- dimethyl-3-ethyl cyclopropane, 1,l,2,2-tetramethyl cyclopropane, 1,l,2,3-tetramethyl cyclopropane, methyl cyclobutane, ethyl cyclobutane, 1,1-dimethyl cyclobutane, 1,2-dimethyl cyclobutane, 1,3-dimethyl cyclobutane, propyl cyclobutane, isopropyl cyclobutane, l-methyl-l-ethyl cyclobutane, 1-methyl-2-ethy1 cyclobutane, 1-methyl-3- ethyl cyclobutane, 1,1,2-trimethyl cyclobutane, 1,1,3-trimethyl cyclobutane, 1,2,3-trime-thyl cyclobutane.

Those alkylcycloalkanes which boil in the range of between about and. F. are of great importance in aviation fuels because of the bon atoms and-wherein the ring carbon atom and the linking carbon atom of the alkyl substituent are in a straight chain of not more than three carbon atoms. One of these is 1,1,2-trimethylcyclopropane and my invention will be illustrated in connection therewith.

According to my invention a unique aviation fuel can be obtained by blends of 1,1,2trimethylcyclopropane and'isooctane. The alkylcyclopropane as the lower boiling ingredient can be used in proportions ranging between about 20 and about 60 percent by volume. Isooctane, preferably hydrocodimer, can be blended in proportions of between about 40 and about 80 percent. An antiknock agent comprisin lead alkyls, e. g. tetraethyl lead, can be added to the blends in conventional quantities varying from small amounts up to the upper limit tolerated by other considerations having to do with engine design. This upper limit at present is fixed at about 4 cc. tetraethyl lead per gallon of fuel. If

desired an aromatic fraction can be included in the blend.

The unique aviation fuel component, 1,1,2-trimethylcyclopropane, is relatively stable to atmospheric oxidation, produces little gum on standing in contact with various metals, and exhibits all the stability characteristics demanded by aviation fuels. It has a boiling point of 127 F. and a Reid vapor pressure of about 8.0 pounds. It has a refractive index of about 1.387, and an API gravity of about 74". By blending this material with for example, an equal volume of isooctane, a superfuel of the proper boiling point specifications will be obtained having a vapor pressure approaching the specification maximum of 7 p. s. i. g

The properties of 1,1,2-trimethylcyclopropane are highly desirable inanaviation fuel for military purposes. -It has a high sensitivity. Sen-, sitive hydrocarbons have the general property of permitting high engine power outputs when a deficiency of air with respect to fuel is supplied to the engine, i. e., under -rich mixture conditions.' This highly sensitive hydrocarbon fuel is particularly advantageous for military aviation.

purposes in pursuit, combat, taking-01f, outrunning, rate of climb, increasing ceiling, etc.

The combination of the desirable properties of extremely high octane number, volatility of the proper magnitude and adequate chemical stability, together withsensitivity, make 1,1,2-trimethylcyclopropane of unique value as an aviation fuel constituent. By my invention I propose to utilize the high blending octane number, the stability, the. sensitivity and the volatility of 1,1,2-trimethylcyclopropane together with commercial isooctane to obtain a superfuel having an octane number of about 100 or higher even in the absence of tetraalkyllead and having much greater octane numbers when small amounts of antiknock agent are employed.

1,1,Z-Trimethylcyclopropane as an example of alkylcyclopropanes having siX carbon atoms in the molecule can be prepared from commercially available diacetone alcohol by reduction to 2- methylpentadiol-2,4, conversion of this to the dihalide, for example, 2-methyl-2,4-dibromopentame, and treatment with zinc in alcohol. Cyclopropane also can be formed from monohalides and sodium, i. e. by the reaction of l-chloro-2,2- dimethyl butane with sodium as described by Whitmore et al., in J. Am. Chem. Soc. vol. 63, page 2633 (1941). I

Some synthetic methods lead to a mixture of isomeric or homologous cyclopropanes or cyclobutanes. I contemplate employing such mixtures as a superfuel component without separation into individual pure hydrocarbons.

The isooctane'refe'rred to herein is the commercial product which may, for instance, be prepared by polymerizing a mixture of isobutylene and other butenes, diluted with butanes, to isooctenes. Subsequently, the isooctenes are hydrogenated to produce a hydrocodimer isooctane fraction. Alkylate isooctane can be prepared by the alkylation of isobutane with butenes or by the dehydroalkylation of. isobutane or by the destructive alkylation of higher branched paraffins, for example by. the sulfuric acid process. By the term isooctane I mean to include both the hydrocodimer and the alkylate isooctane.

When an alkylcycloalkane having five, six or, seven carbon atoms in the molecule is. blended with between about 20% and 60%"by volume of isooctane a very satisfactory aviation fuel can be obtained. a

Although certain embodiments of my invention have been described, it is to be understood that my invention is not limited thereto but only by the appended claim.

I claim:

An aviation combat fuel showing both a high supercharge octane number and a high rich mixture response comprising a blend of between about 40% and commercial isooctane and between about 20% and 60%v of 1, 1,2-trimethylcyclopropane.

ROBERT MARSC HNERe 

